Okajimas Fol, anat. jap., 53: 359-382, 1977 On the Mental Arteries and Lower Incisor Branch of the Dog By Mitsutaka Mizutani Department of Anatomy, Osaka Dental University, Osaka (Director Prof. Y. Ohta) With two text-figures and 19 figures in 5 plates —Received for Publication, May 29, 1976— Preface The inferior alveolar artery terminates into the mental artery and the incisor branch in man. There have been very few works on the distributing features of these termini, especially, the communication between the inferior alveolar arteries of the left and right sides. Some scholars, however, have attempted to make experimental investigations on anastomoses between the inferior alveolar arteries of laboratory animals. This work will deal with distribution features of the mental arteries and the incisor branch and the communication between these vessels of both sides in the lower lip and mandible of the dog. It may be most significant to make a detailed study on the termination of the inferior alveolar artery of the dog's symphysis which can be separated easily. In addition to them, the author has tried to survey the number and location of the mental foramina because there has been only description of them by Miller (1964). Material and Methods Thirty-one mandibles of dogs were used in the study of the mental foramina. Sixty-five adult dogs were used for the observation of the inferior alveolar artery and its ramification. The acryl plastic was injected into the vasculature of the head through the common carotid arteries by employing the plastic injection method of Taniguchi, Ohta and Tajiri (1952, 1955). Sixty injected heads were made into corrosion specimens of the carotid system. When these heads have been digested with 359 360 Mitsutaka Mizutani sodium hydroxide and washed, special attention was given to the pro- tection of the mandible and teeth. Four injected heads were preserved in the formalin solution for the dissection. The anterior half of the mandible of the remained one head was fixed with the formalin solution, decalcified and embedded in celloidin. The block was cut to produce serial 250p sections on the frontal surface and every tenth section at 20p was stained with hematoxylin-eosin. Observations I. Mental foramina Three mental foramina are observed ; the anterior, the middle and the posterior, which stand in a line anteroposteriorly on the lateral surface of the mandibular body at the level of the middle of it. 1. Anterior mental foramen (about 1mm in diameter) In all cases observed, it is located about 6 mm inferior to the alveolar margin between I, and I, and opens upward. 2. Middle mental foramen (about 3.5 mm in diameter) In all cases observed, it, the largest, is located about 10 mm inferior to the alveolar margin between P1 and P2 and opens forward. 3. Posterior mental foramen In 44 of 62 sides, it (about 1.5 mm in diameter), one in number, is located about 10 mm inferior to the alveolar margin between the mesial root apex of P3 and its distal apex and opens upward. In nine cases (2 mandibles and 5 sides) two posterior mental foramina (about 1.0 mm in diameter) are seen in each of these sides. The distal posterior mental foramen is located between the distal apex of P2 and the mesial apex of 133, about 5 mm posterior to the middle foramen, and opens superoanteriorly. The proximal foramen is located near the mesial apex of P4 and opens superoposteriorly. These four foramina stand in a line (Fig. 4). In different nine cases (2 mandibles and 5 sides) any posterior foramen is not observed but only two foramina in each of these sides (Fig. 5). II. Mental arteries The arteries in the dog consist of three ; the anterior, the middle and the posterior. The posterior mental artery is a branch of the inferior alveolar artery, and terminal branches of which are the middle mental artery and the incisior branch, from which the anterior mental arises (Fig. 1). 1. Posterior mental artery The artery (0.24-0.56 mm, M. 0.40 mm in diameter), observed one in number in 65 of 120 sides, arises from the superior or lateral wall of On the Mental Arteries and Lower Incisor Branch of the Dog 361 the inferior alveolar artery (0.68-1.12 mm, M. 0.88 mm) right beneath between the root apecies of P3 and P4 in the inferior alveolar canal (Figs. 1 and 6). It runs anterolaterally and leaves the posterior mental foramen with the satellite vein and nerve. The arising point some- times moves proximally right beneath the mesial apex of M1 and the artery runs in company with the parent artery in the superior side of it and leaves the posterior mental foramen after bending laterally at the apex of P4 (Fig. 7). In 9 of the 65 cases, the artery is so fine that it terminates in the canal or around the posterior mental foramen. Before the artery leaves the foramen, it gives off the dental and alveolar branches to Pa and P4 (Figs. 1 and 6). In 37 of 120 sides, the artery is not observed, that is, the posterior mental foramen is not observed, or even if the foramen exists, the posterior mental nerve and thick vein pass through the foramen (Fig. 8). In 18 cases of 120 sides, two posterior mental arteries are seen (Fig. 9). The proximal arises from the superolateral wall of the inferior alveolar at the distal apex of P4 and runs anterolaterally, giving off the dental and alveolar branches to P3 andF4, then leaves the proximal posterior mental fora- men superoposteriorly. The distal arises from the superior wall of the inferior alveolar at the mesial apex of P3 and runs anterolaterally, giving off the dental and alveolar branches to P2, then leaves the distal posterior mental foramen superoanteriorly. Immediately after leaving the foramen, the artery spreads into the periosteal, the gingival and the inferior labial branches (Figs. 2 and 10). The periosteal branches (0.10-0.22 mm, M. 0.15 mm) supply the periosteum inferior to the foramen and anastomose with the periosteal branches of the submental (Fig. 10). The gingival branches (0.10-0.24 mm, M, 0.16 mm), 2-5 in number, arborize upward from the foramen to supply gingivae of P2, P8 and P4, then anastomose with peripheries of the sublingual artery beyond intergingival papillae (Fig. 11). The inferior labial branches (0.14-0.31 mm, M. 0.24 mm), 2-4 in number, consist of Fig. 1. The medial view. The schematic illustration of the ramification of the mental arteries and the incisor branch. See the key to abbreviations of Page 370. 362 Mitsutaka Mizutani Fig. 2. The lateral view. The schematic illustration of the distributing feature of the mental arteries and the inferior labial arterial arch. See the key to abbreviations of Page 370. ones (0.17-0.31 mm, M. 0.25 mm) passing superoanteriorly and others (0.14-0,29 mm, M. 0.22 mm) passing superoposteriorly (Fig. 12). The former communicates with muscular branches of the posterior branch of the middle mental artery and the latter with branches of the inferior labial artery in the labiogingival portion. These communications take part in the formation of the inferior labial arterial arch, from which the labial marginal branches (5-10 in number) arise upward to the conical papillae of the lower lip lying opposite P2 and P3. Usually one or two branches enter each papilla. In addition, many cutaneous and muscular branches are seen. 2. Middle mental artery The inferior alveolar artery bifurcates into the incisor branch and the middle mental artery 3-10 mm posterior to the apex of the canine between the root apecies of P2 and P3 (Figs. 1 and 6). The artery (0.53-1.05 mm, M. 0.75 mm) bends anterolaterally and passes lateral to the root of the canine toward the middle mental fora- men. It finally leaves the foramen with the satellite nerve forward. In the inferior alveolar canal it gives off the dental and alveolar bran- ches to P1 and P2 and twigs to the satellite nerve (Figs. 1 and 6). The artery divides into the anterior and posterior branches before leaving the foramen in 70 of 120 sides (Fig. 11), just on the margin of it in 35 cases (Fig. 10) and 1-3 mm distal to it in 15 cases (Fig. 13). a) Anterior branch The branch (0.53-0.81 mm, M. 0.63 mm) passes forward in the mental muscle with the middle mental nerve and bends superomedially medial to the canine, and finally reaches the symphysis 10-15 mm inferior to On the Mental Arteries and Lower Incisor Branch of the Dog 363 the margin of the lower lip, where an arterial arch is formed with the fellow of the opposite side. The arch, being rather distinct (0.24- 0.67 mm, M. 0.47 mm in diameter), faces its convex upward and forward, and takes part in the formation of the inferior labial arterial arch which is located between the anterior mental foramina of the left and right sides (Figs. 14 and 15). From the arch, the superior, the inferior and the gingival branches diverge. The superior branches (0.10-0.36 mm, M. 0.20 mm), 4-10 in number, arise from the superior wall of the arch. Each of them, by anastomosing with the adjacent one, makes many loops. Such a loop formation is repeated and finally develops into a coarse arterial network in the lower lip between the canines of both sides (Figs.